CARDIOVASCULAR JOURNAL OF AFRICA • Vol 23, No 9, October 2012
488
AFRICA
re-coarctation of the aorta have traditionally been made based on
the judgment of the character of the femoral pulse. Also known
as a secondary event, absent, weakened or delayed femoral
pulses occur as a result of obstruction in aortic coarctation.
The pressure drop across the obstruction (the gradient),
pressure half-time, and diastolic flow are widely used but
inaccurate indices to diagnose aortic coarctation. They can
be affected by many other factors such as cardiac output,
26
lesion length,
27
the presence of collateral networks,
26
and aortic
compliance.
28
Stent implantation has been used as a reliable treatment for
coarctation of the aorta. It has several advantages, rendering it
superior to angioplasty alone.
29
The effect of stents on blood flow
dynamics are not well known. Moreover, despite the importance
of close follow up to evaluate complications and the long-term
effect on the blood pressure of these patients, there are no
adequate long-term follow-up indices for these patients.
Therefore the present study was carried out to find reliable,
quantitative Doppler echocardiographic indices for assessment
of the severity of coarctation of the aorta before stenting and
comparing these indices with the post-stenting condition. This
would provide a valuable profile to indicate successful stent
implantation.
All previous methods, including monitoring the blood
pressure, two-dimensional echocardiography, cardiac magnetic
resonance (CMR) and angiography have failed to give favourable
results. Persistent hypertension, even in the absence of a recurrent
or residual stenosis,
25,30
insufficient anatomical evaluation of
two-dimensional echocardiography,
31
and disrupted MRI by
metallic artifacts (or noise) have limited the value of these
indices to assess the patient at post-intervention follow up.
32
Furthermore, angiography as an invasive procedure has known
complications.
Doppler echocardiography overcomes these problems in the
follow up of such patients. However, echocardiography may be
less sensitive than angiography, spiral computed tomography and
MRI in detecting aneurysms after stent placement.
32
Based on our results, the Doppler echocardiographic profile
was found to be valid for differentiating significant coarctation
from the normal condition (after stenting), with high diagnostic
values. As demonstrated in the results, continuous flow was
significantly decreased from before to after stenting in both
the descending and abdominal aorta. Moreover, monophasic
systolic flow was shown to increase significantly after stenting.
In comparison with a few similar studies,
4,20
we assessed more
indices, which we will discuss below.
According to our results, aortic pulse delay decreased after
stenting. The results also showed that a pulsatility index of
<
1.21
was suggestive of significant coarctation of the aorta. This
cut-off point was calculated as
<
2
in a study by Silvilairat
et al
.
33
Currently, it is known that obstructed blood flow due to aortic
coarctation leads to pressure drop and loss of the pulse wave
distal to the stenosis. This can be observed by echocardiography
typically as decreased pulsatility of the abdominal aorta after
cardiac systole.
34
Early and late diastolic velocities were found to be significant
markers in the assessment of the severity of coarctation. In
addition, mean peak gradient of the descending aorta was
significantly reduced by as much as 58% following stenting. This
could be the result of changed flow dynamics along the stent.
4
However, in some patients, there was an under- or overestimation
of the pressure gradient across the coarctation site on Doppler
echocardiography. As mentioned, these are affected by other
factors, such as cardiac output,
26
lesion length,
27
the presence
of collateral networks,
26
and aortic compliance.
28
Therefore
pressure gradient alone as an index of aortic narrowing is often
inadequate.
Although the mean velocity in both the descending and
abdominal aorta significantly decreased after stenting, the
difference was more significant in the descending aorta, with an
approximately 45% reduction. Similarly, the acceleration time
in the descending aorta was different from the corresponding
measurement in the ascending aorta in coarctation.
31
This is
manifested clinically by radial femoral delay and diminished
pulses distal to the coarctation. After stent implantation, the
acceleration time showed statistically significant decreases in
both the descending and abdominal aorta.
Based on our findings, the velocity–time integral and time
to peak systolic velocity can be also used as new markers of
significant coarctation. Both indices significantly decreased
after stenting. We also found pressure half-time indices (systolic
and diastolic velocity half-times, systolic and diastolic pressure
half-times) can be used to assess the severity of coarctation,
with sensitivities of 87 and 81.8% and specificities of 100 and
87%
for the abdominal aorta and descending aorta, respectively.
These findings were in keeping with the results of previous
investigations by Carvalho
et al
.
35
and Tan
et al
.,
4
which reported
a significant effect of coarctation of the aorta on these indices.
A study by Lim and Ralston however was in disagreement with
regard to systolic indices.
36
Diastolic velocities (DVs) and diastolic pressure decays have
been shown to provide invaluable information for assessing the
severity of coarctation.
35-37
The index of D/S ratio velocity was
first used by Tan
et al
.
4
as a marker of significant coarctation.
They demonstrated that a D/S ratio velocity of
>
0.53
had
a sensitivity of 100% and specificity of 96% for detecting
significant aortic coarctation. They believed that by correlating
diastolic with systolic velocity, this ratio would be less affected
by variations in heart rate, stroke volume, systemic blood
pressure and aortic compliance.
4
However, we found a lower cut-off point for D/S ratio
velocity. The D/S ratio of
>
0.365
in the descending aorta had
a sensitivity of 95.7% and specificity of 87%, whereas the ratio
of
>
0.43
in the abdominal aorta had a sensitivity of 81.8% and
specificity of 91.3% in defining significant coarctation of the
aorta. D/S ratio velocity appears to be a good marker of this
condition. Recently, the D/S ratio as a non-invasive measurement
of coronary flow velocity has been used to evaluate left anterior
descending artery (LAD) stenosis. By contrast with the aorta,
the D/S ratio was found to be significantly lower in patients with
more critical stenosis of the LAD.
38
Besides evaluation of the diagnostic value of the
echocardiographic indices, a correlation analysis was also
performed in our study to assess the relationship between the
severity of coarctation before stenting and the echocardiographic
indices. As shown, PHT and VTI of the abdominal aorta and
EDV, EDV, PHT, mean velocity and mean peak gradient of the
descending aorta correlated significantly with the peak gradient
in the coarctation site, measured by catheterisation prior to stent
implantation.
